Segment Data - Schedule of Segment Data (Details) - USD ($) $ in Millions		3 Months Ended				9 Months Ended
		Sep. 30, 2023		Sep. 30, 2022		Sep. 30, 2023		Sep. 30, 2022
Segment Reporting Information [Line Items]
Revenues from services	[2]	$ 4,675.6	[1]	$ 4,800.9	[1]	$ 14,284.0	[3]	$ 15,018.3	[3]
Corporate expenses		(37.4)		(37.0)		(110.8)		(114.8)
Intangible asset amortization expense		(8.7)		(9.1)		(26.2)		(28.1)
Operating profit		69.8		161.5		295.3		480.9
Interest and other expenses, net		(15.1)		(4.7)		(34.4)		(14.1)
Earnings before income taxes		54.7		156.8		260.9		466.8
Americas
Segment Reporting Information [Line Items]
Operating unit profit	[4]	37.9		71.1		129.7		224.8
Southern Europe
Segment Reporting Information [Line Items]
Operating unit profit	[4]	84.4		100.3		266.9		307.2
Northern Europe
Segment Reporting Information [Line Items]
Operating unit profit	[4]	(30.6)		12.8		(35.3)		26.9
Northern Europe and APME
Segment Reporting Information [Line Items]
Operating unit profit	[4]	115.9		207.6		432.3		623.8
Consolidation Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from services		(23.4)		(19.7)		(64.1)		(55.0)
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenues from services		(23.4)	[1]	(19.7)	[1]	(64.1)	[3]	(55.0)	[3]
United States | Americas
Segment Reporting Information [Line Items]
Revenues from services		752.6		886.6		2,259.3		2,679.9
Other Americas | Americas
Segment Reporting Information [Line Items]
Revenues from services		358.7		353.2		1,080.9		1,073.8
France | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		1,209.9		1,159.5		3,657.4		3,590.1
Italy | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		413.7		395.1		1,293.7		1,294.4
Other Southern Europe | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		485.1		485.2		1,452.4		1,550.6
Reportable subsegments | Americas
Segment Reporting Information [Line Items]
Revenues from services		1,111.3	[1]	1,239.8	[1]	3,340.2	[3]	3,753.7	[3]
Reportable subsegments | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		2,108.7	[1]	2,039.8	[1]	6,403.5	[3]	6,435.1	[3]
Reportable subsegments | Northern Europe
Segment Reporting Information [Line Items]
Revenues from services		914.2	[1]	954.1	[1]	2,834.3	[3]	3,075.7	[3]
Reportable subsegments | APME
Segment Reporting Information [Line Items]
Revenues from services		564.8	[1]	586.9	[1]	1,770.1	[3]	1,808.8	[3]
Operating unit profit	[4]	24.2		23.4		71.0		64.9
Reportable subsegments | Northern Europe and APME
Segment Reporting Information [Line Items]
Revenues from services		4,699.0	[1]	4,820.6	[1]	14,348.1	[3]	15,073.3	[3]
Reportable subsegments | United States | Americas
Segment Reporting Information [Line Items]
Revenues from services	[5]	752.6	[1]	886.6	[1]	2,259.3	[3]	2,679.9	[3]
Operating unit profit	[4]	25.4		54.7		82.7		177.7
Reportable subsegments | Other Americas | Americas
Segment Reporting Information [Line Items]
Revenues from services		358.7	[1]	353.2	[1]	1,080.9	[3]	1,073.8	[3]
Operating unit profit	[4]	12.5		16.4		47.0		47.1
Reportable subsegments | France | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		1,209.9	[1]	1,159.5	[1]	3,657.4	[3]	3,590.1	[3]
Operating unit profit	[4]	47.9		56.6		142.3		168.5
Reportable subsegments | Italy | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		413.7	[1]	395.1	[1]	1,293.7	[3]	1,294.4	[3]
Operating unit profit	[4]	27.0		29.0		94.0		93.5
Reportable subsegments | Other Southern Europe | Southern Europe
Segment Reporting Information [Line Items]
Revenues from services		485.1	[1]	485.2	[1]	1,452.4	[3]	1,550.6	[3]
Operating unit profit	[4]	$ 9.5		$ 14.7		$ 30.6		$ 45.2

[1] Certain service line revenues for the United States and Northern Europe were reclassified for the 2022 comparative period to align with the current period presentation. In the United States, $58.4 was reclassified from Outcome-Based Solutions and Consulting to Staffing and Interim. In Northern Europe, $24.8 was reclassified from Staffing and Interim to Outcome-Based Solutions and Consulting.

[2] Our consolidated revenues from services include fees received from our franchise offices of $3.8 and $4.4 for the three months ended September 30, 2023 and 2022, respectively, and $11.0 and $11.9 for the nine months ended September 30, 2023 and 2022, respectively. These fees are primarily based on revenues generated by the franchise offices, which were $243.5 and $264.0 for the three months ended September 30, 2023 and 2022, respectively, and $744.3 and $804.8 for the nine months ended September 30, 2023 and 2022, respectively.

[3] Certain service line revenues for the United States and Northern Europe were reclassified for the 2022 comparative period to align with the current period presentation. In the United States, $171.6 was reclassified from Outcome-Based Solutions and Consulting to Staffing and Interim. In Northern Europe, $90.0 was reclassified from Staffing and Interim to Outcome-Based Solutions and Consulting.

[4] We evaluate segment performance based on operating unit profit (“OUP”), which is equal to segment revenues less cost of services and branch and national headquarters operating costs. This profit measure does not include goodwill and intangible asset impairment charges or amortization of intangibles related to acquisitions, corporate expenses, interest and other expense amounts or income taxes.

[5] In the United States, revenues from services included fees received from the related franchise offices of $3.1 and $3.7 for the three months ended September 30, 2023 and 2022, respectively, and $8.9 and $9.7 for the nine months ended September 30, 2023 and 2022, respectively. These fees are primarily based on revenues generated by the franchise offices, which were $98.6 and $121.9 for the three months ended September 30, 2023 and 2022, respectively, and $298.7 and $360.8 for the nine months ended September 30, 2023 and 2022, respectively.